Über dieγ- und δ-Modifikationen des Natriumdisilikates, Na2Si2O5

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Abstract
At room-temperature γ Na 2 Si 2 O 5 is monoclinic, pseudotetragonal with the lattice constants a = 23.46 4 Å, b = 7.08 7 Å, c = 26.12 0 Å, β = 116°41′ and 8 formula units in the pseudotetragonal cell. Due to disorder there was no possibility to distinguish between the space groups Pc – C s 2 or P 2/ c – C 2 h 4 and P 2 1 / c – C 2 h 5 . The pseudotetragonal symmetry is I 4 1 / a – C 4 h 6 . One of the high-temperature forms of γ Na 2 Si 2 O 5 probably is tetragonal. A new orthorhombic modification of sodium disilicate, δ Na 2 Si 2 O 5 , was found with a = 12.07 0 Å, b = 8.37 5 Å, c = 4.84 0 Å, Z = 4. The space group is Pnmm – D 2 h 13 or Pn 2 1 m – C 2 v 7 . Whereas structural relations are to be expected between δ and β Na 2 Si 2 O 5 , such relations to silicate structures with “Zweiereinfachschichten” cannot be deduced simply from lattice constants for the γ modification.

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